the Impact of Noise on Requirements of Anesthetics During General Anesthesia

The investigators hypothesize that the noise level in the operating theatre influences the patients\' requirements of anesthetics. Study subject are patients undergoing abdominal surgery in combined general and epidural anesthesia. Analgesia is maintained by epidural injections of sufentanil and ropivacaine whereas general anesthesia is maintained using the inhalational anesthetic desflurane. Desflurane requirements are adjusted using neuromonitoring (BIS-Index). Intraoperative noise levels are recorded. Patients are randomized to receive hearing protections or not.